Iatrophysics

A key component of iatrophysical anatomy was the study of particles. This was particularly influenced by 17th century developments in microbiology, the most prominent being the microscope. Antonie von Leeuwenhoeck was a Dutch scientist who is known for his use of the microscope for identifying single-celled organisms. He was also the first to observe muscle fibers, bacteria, spermatozoa and blood flow in capillaries.[4] Another famous figure in microbiology at the time was Robert Hooke, an English scientist most famous for his use of the microscope for the discovery of cells.[5] In his most famous work, Micrographia (1665), he attributed “occult properties” as elementary “contrivances of nature”. Like Galileo Galilei, he shared an iatrophysical viewpoint and saw living organisms as groups of small machines. The development of the microscope was largely influential in this view.[6]

Machines were used as models by Iatrophysicists to quantitatively describe linear and rotational motion of various biological systems such as human limbs and animals. Some models came into existence before Isaac Newton's formulation of his three laws in classical mechanics, drawing on basic principles of statics and dynamics to represent how a biological system behaved. Giovanni Borelli was prolific in applying mechanics to a wide variety of humans and animals in different degrees of activity, drawing upon an array of simple machines and models for translational and rotational motion and equilibrium.[7][8][9]

Iatrophysicists were also interested in studying how bodily liquids and gases were processed. They sought to understand how blood circulated throughout the body and what effects it made on the body. System consisted of arteries, veins, and vasculature verified through experiment and microscope by Marcello Malpighi's observations of capillaries in animal lung tissue. Albrecht von Haller, as did Borelli, postulated that friction from the blood on vessel walls lead to body heat and even fever. A hydraulic model for motion by René Descartes implied the body had a system that maintained flow between the brain and muscles in equilibrium state through nerves and blood vessels.[8]

One prominent iatrophysicist was Giovanni Borelli, who modeled the human body, various animals, and their motions using mechanical principles.[7][10] A colleague of Marcello Malphigi, Borelli was a mathematician who made connections between what he observed in living things and inanimate but relatively simple systems. He dissected animals and examined how muscles were to increase mechanical advantage, observed how a variety of living things performed different movements and activities such as running, carrying loads, swimming, and flying naturally rather than by his intervention, and devised simple methods to calculate a person's center of mass. He also devised relatively simple experiments and devices to make his observations such as a plank and rod for center of mass and a spirometer for volume of air. At the end of his life, his work culminated in De Motu Animalium (1679), a publication showcasing his investigations in similarities and differences in muscles across living things and his understanding of the underlying mechanism of muscle contraction, expansion via influx of fluids or gases released from nerves. He also attempted to describe more complicated processes such as nerve transmission and digestion.[8][11]

Another notable iatrophysicist was the French philosopher and mathematician René Descartes, who, as a consequence of his philosophy asserting that the human body and soul are two dual entities, treated the human body as a machine that could be quantified, disassembled, and studied. He attempted to model various phenomena such as the brain, movement, sleep, circulation, and senses with analogies to inanimate objects such as reservoirs, pipes, lenses and steam engines that often sought to maintain an equilibrium for certain states. Some of his claims often were independent of physical observation of the organ or body in question and emphasized what he deemed as "simple" or "rational" rather than reality. For example, he asserts that blood circulates throughout the body by expanding as vapor by the heart's heat rather than from contraction.[7][8]

William Harvey postulated blood flow as a closed, continuous loop that run throughout body that contained a certain quantity of blood. To test his claim, Harvey dissected human corpses and animals and, based on his anatomical findings, devised a simple demonstration of how arteries and veins continuously carried blood throughout the body. Taking advantage of the fact that arteries and veins were at different depths below the skin, he tied a person's arm and had them squeeze a bar to shunt blood from arteries to veins, indicating that blood somehow traveled along arteries and into veins. His claim was elucidated by Malphigi's discovery of capillaries and how they were interconnected with arteries and veins.[7][8]

One of the most influential iatrophysicists was Hermann Boerhaave, a Dutch physician and chemist at the Leiden University. Like other iatrophysicists, he viewed physiology as a mechanism. While he disagreed with the idea that the body and the mind were connected, he attributed everything related to the body to extension, impenetrability, or motion.[6]

Francis Glisson was known for his work on circulation of the blood, the mechanisms of the nervous system, and hereditary diseases. He was largely influenced by Harvey's work on the sentient nature of blood and his work demonstrates iatrophysical ideology particularly through his views of attraction and irritability, or the concept of how the body fibers react to irritation. In his work, Anatomia hepatis, he argues that branches cross, and carried blood is separated in the liver. This in turn is sucked up by biliary vessels through an attraction that Glisson attributes as similar, magnetic, or natural.[12]

Albrecht von Haller was another prominent iatrophysicist, who like Glisson, focused on physiology as mechanisms of body fibers. He shared Glisson's views on irritability, but unlike Glisson, attributed the reaction to external stimuli solely to body fibers, and not in the inherent power of matter as Glisson had suggested. In his work Physiologiae Corporis Humani (1757–1766), he described organs and muscles of the body as interwoven fibers. His viewpoints on muscles were that they had a contractile tendency which he termed vis mortua, or dead power. He attributed this muscle contraction to irritability, which he described as being an inherent power. He particularly made the distinction between irritability and sensibility, irritability being the power of muscular contraction and sensibility being nerve impulse. Therefore, a part was irritable if it contracted upon contact, and sensible if the contact impacted the mind.[6]

Santorio Santorio was a Venetian doctor who, in attempt to quantify human digestion, carefully measured his food/water intake and excretion weight over many years. To establish a mathematical relationship between food/water intake and excretion, Santorius designed a special chair that had a balance that weighed a subject's meal and consequent excrement. Based on these measurements, he then calculated the net change in weight for each day. In addition to knowing what he took in, he also analyzed the contents of his excretions and secretions, categorizing it by type and origin. He also made other clinical instruments to measure other medical quantities such as temperature and pulse.[7][8]

Nicolas Steno was a Danish scientist who developed a purely mechanical and geometrical model of muscle. In this model, he treated a muscle as an interwoven yet simple network of long fibers, forming a uniform and robust geometric shape. Contraction was then explained as the reshaping of this network to either shorten or lengthen along one direction, thus the muscle changed shape at a fixed volume by only changing the angles between each fibre. This explanation of contraction, and his consequent theory that the heart contracted by many of its fibers shortening and lengthening, was considered radical. The most popular explanation, supported by well known Iatrophysicists such as Descartes and Borelli, asserted that the heart contracted from its fibers inflating themselves through a chemical reaction.[8][13]